1. They monitor their emotions.

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People often assume mentally strong people suppress their emotions, Morin says, but they are actually acutely aware of them.

"They monitor their emotions throughout the day and recognize how their feelings influence their thoughts and behaviors," she says. "They know sometimes reaching their greatest potential requires them to behave contrary to how they feel."

2. They practice realistic optimism.

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Having a positive outlook all the time is impossible, and too much negativity is counterproductive.

Mentally strong people "understand that their thoughts aren't always true, and they strive to reframe their negativity," Morin says. "They replace exaggeratedly negative thoughts with a more realistic inner monologue."

3. They solve problems.

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To put it simply, "mentally strong people refuse to engage in unproductive activities," Morin says. Instead of sitting there complaining about your bad day at work and wishing bad things wouldn't happen, evaluate why something went wrong and fix it. Learn how to calculate risk and move forward from there, she says.

4. They practice self-compassion.

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Rather than beating themselves up for making mistakes, mentally strong people practice self-compassion and speak to themselves as they would speak to a good friend, Morin says.

"They respond to their inner critic as if they were standing up to the schoolyard bully," she says. "They forgive themselves for mistakes and cheer themselves on as they work toward their goals."

5. They set healthy boundaries.

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One thing mentally strong people avoid is giving away their power. People give away their power when they lack physical and emotional boundaries, Morin says. They can establish healthy boundaries, however, by behaving assertively, she says.

"They accept full responsibility for how they think, feel, and behave," she says, "and they refuse to let other people dictate whether they're going to have a good day or a bad day."

6. They manage their time wisely.

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Mentally strong people describe time as a finite resource, Morin says. That's why they try to use it in a meaningful way. "Rather than waste energy dwelling on the past or resenting other people for taking up their time, they focus on more productive activities," she says.

7. They strive to fulfill their purpose.

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Successfully fulfilling your purpose in life takes time. Mentally strong people understand this and focus on the big picture, keeping in mind that today's choices impact their future.

8. They seek to grow stronger.

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"Mentally strong people view everyday challenges as opportunities to grow stronger," Morin says. Additionally, they never settle or consider themselves strong enough. There is always room for improvement.

"They know that just like physically strong people need to work out to stay in good shape, they need to keep working out their mental muscles to prevent atrophy," she says.

9. They monitor their progress.

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Doing whatever it takes to improve can help you reach your greatest potential. It starts with acknowledging your weaknesses and having a "no excuses" approach.

"Rather than make excuses for their mistakes or failures, they seek explanations that will help them perform better moving forward," Morin says.